Methods and systems for forming thin films

ABSTRACT

A method and apparatus for the deposition of thin films is described. In embodiments, systems and methods for epitaxial thin film formation are provided, including systems and methods for forming binary compound epitaxial thin films. Methods and systems of embodiments of the invention may be used to form direct bandgap semiconducting binary compound epitaxial thin films, such as, for example, GaN, InN and AlN, and the mixed alloys of these compounds, e.g., (In, Ga)N, (Al, Ga)N, (In, Ga, Al)N. Methods and apparatuses include a multistage deposition process and system which enables rapid repetition of sub-monolayer deposition of thin films.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation application and claims priority toU.S. Application Ser. No. 13/025,046 filed on Feb. 10, 2011, which isherein incorporated by reference for all purposes.

BACKGROUND OF THE INVENTION

The growth of high-quality crystalline semiconducting thin films is atechnology of significant industrial importance, with a variety ofmicroelectronic and optoelectronic applications, including lightemitting diodes and lasers. The current state-of-the-art depositiontechnology for gallium nitride (GaN), indium nitride (InN) and aluminumnitride (AlN) thin films, their alloys and their heterostructures (also“InGaAlN” herein) is metal-organic chemical vapor deposition (“MOCVD”),in which a substrate is held at high temperature and gases which containthe elements comprising the thin film flow over and are incorporatedinto the growing thin film at the surface of the wafer. In the case ofGaN, the state-of-the-art may include growth temperatures ofapproximately 1050° C. and the simultaneous use of ammonia (NH₃) and aGroup III alkyl precursor gas (e.g., trimethylgallium, triethylgallium).

While methods exist for forming InGaAlN films, there are limitationsassociated with current methods. First, the high processing temperatureinvolved in MOCVD may require complex reactor designs and the use ofrefractory materials and only materials which are inert at the hightemperature of the process in the processing volume. Second, the hightemperature involved may restrict the possible substrates for InGaAlNgrowths to substrates which are chemically and mechanically stable atthe growth temperatures and chemical environment, typically sapphire andsilicon carbide substrates. Notably, silicon substrates, which are lessexpensive and are available in large sizes for economic manufacturing,may be less compatible. Third, the expense of the process gases involvedas well as their poor consumption ratio, particularly in the case ofammonia, may be economically unfavorable for low cost manufacturing ofInGaAlN based devices. Fourth, the use of carbon containing precursors(e.g., trimethylgallium) may result in carbon contamination in theInGaAlN film, which may degrade the electronic and optoelectronicproperties of the InGaAlN based devices. Fifth, MOCVD reactors may havea significant amount of gas phase reactions between the Group III andthe Group V containing process gases. The gas phase reactions may resultin undesirable deposition of the thin film material on all surfaceswithin the reaction volume, and in the undesirable generation ofparticles. The latter may result in a low yield of manufactured devices.The former may result in a number of practical problems, includingreducing the efficacy of in-situ optical measurements of the growingthin film due to coating of the internal optical probes and lenssystems, and difficulty in maintaining a constant thermal environmentover many deposition cycles as the emissivity of reactor walls willchange as deposition builds up on the reactor walls. These problems maybe common to all the variants of MOCVD, including plasma enhanced MOCVDand processes typically referred to as atomic layer deposition (ALD) oratomic layer epitaxy (ALE).

Other methods for forming InGaAlN thin films include plasma-assistedmolecular beam epitaxy (“PAMBE”), in which fluxes of evaporated Ga, In,or Al are directed in high vacuum at a heated substrate simultaneouslywith a flux of nitrogen radicals (either activated molecular nitrogen,atomic nitrogen, or singly ionized nitrogen atoms or molecules) from anitrogen plasma source. The method may be capable of producing highquality InGaAlN thin films and devices, but the method may suffer from atendency to form metal agglomerations, e.g., nano- to microscopic Gadroplets, on the surface of the growing film. See, for example,“Homoepitaxial growth of GaN under Ga-stable and N-stable conditions byplasma-assisted molecular beam epitaxy”, E. J. Tarsa et al., J. Appl.Phys 82, 11 (1997), which is entirely incorporated herein by reference.As such, the process may need to be carefully monitored, which mayinherently result in a low yield of manufactured devices.

Other methods employed to make GaN films include hydride vapor phaseepitaxy, in which a flow of HCl gas over heated gallium results in a thetransport of gallium chloride to a substrate where simultaneous exposureto ammonia results in the growth of a GaN thin film. The method mayrequire corrosive chemicals to be used at high temperatures, which maylimit the compatible materials for reactor design. In addition, thebyproducts of the reaction are corrosive gases and solids, which mayincrease the need for abatement and reactor maintenance. While themethod may produce high quality GaN films at growth rates (tens tohundreds of microns per hour have been demonstrated, exceeding thosecommonly achieved with MOCVD), the reactor design and corrosive processinputs and outputs are drawbacks.

SUMMARY OF THE INVENTION

In an aspect of the invention, methods for forming GroupIII-V-containing thin films are provided. Methods for forming GroupIII-V thin films may minimize, if not eliminate, thin filmcontamination, thereby providing for forming high quality Group III-Vthin films.

In one embodiment, a method for forming a Group III-V thin filmcomprises contacting a substrate in a first reaction space with a GroupIII precursor to form a Group III metal thin film at sub-monolayercoverage; and contacting the substrate in a second reaction space with aGroup V precursor, thereby forming a Group III-V thin film.

In another embodiment, a method for forming a Group III-V thin film on asubstrate, comprises alternately and successively contacting a substratewith a Group III metal precursor and a Group V precursor, wherein thesubstrate is contacted with a Group III metal precursor and the Group Vprecursor in separate reaction spaces, and wherein contacting thesubstrate with the Group III metal precursor forms a Group III metalthin film at sub-monolayer coverage.

In another embodiment, a method for forming a Group III-V thin film on asubstrate, comprises providing a Group III metal layer on a substrate,the Group III metal layer having one or more Group III metals at apre-wetting coverage; and contacting the Group III metal layer with aGroup V precursor.

In another embodiment, a method for forming a Group III-V thin film on asubstrate, comprises (a) disposing a substrate in a first reactionspace; (b) directing one of a first Group III precursor and a firstGroup V precursor into the first reaction space; (c) disposing thesubstrate in a second reaction space; (d) directing the other of thefirst Group III precursor and the first Group V precursor into thesecond reaction space; and (e) repeating steps (a)-(d) until a Group IIImetal nitride thin film of predetermined thickness is formed, whereindirecting the first Group III precursor into the first reaction space orthe second reaction space forms a Group III metal thin film atsub-monolayer coverage. In some embodiments, substrate may be disposedin a reaction space by moving the substrate to the reaction space (e.g.,by rotating a susceptor having the substrate to the reaction space). Inother embodiments, the substrate may be disposed in a reaction space bybringing the reaction space to the substrate (e.g., by rotating areaction chamber having the reaction space).

In another embodiment, a method for forming a Group III-V thin film on asubstrate, comprises: (a) moving a substrate to a first reaction space;(b) contacting the substrate with one of a first Group III precursor anda first Group V precursor in the first reaction space; (c) moving thesubstrate to a second reaction space; (d) contacting the substrate withthe other of the first Group III precursor and the first Group Vprecursor in the second reaction space; and (e) repeating steps (a)-(d)until a Group III-V thin film of predetermined thickness is formed,wherein contacting the substrate with the first Group III precursorforms a Group III metal thin film at sub-monolayer coverage.

In one embodiment, the Group III-V thin film may comprise epitaxiallayers of gallium nitride and/or indium gallium nitride. In anotherembodiment, the Group III-V thin film may comprise epitaxial layers ofaluminum nitride, aluminum gallium nitride, gallium nitride, indiumgallium nitride, or aluminum indium gallium nitride.

In another aspect of the invention, systems and apparatuses for formingGroup III-V thin films are provided. In one embodiment, an apparatus fordepositing a Group III-V thin film on a target (e.g., substrate)comprises a first reaction space and a second reaction space, the firstreaction space fluidically separated from the second reaction space; asusceptor for bringing a target in contact with each of the first andsecond reaction spaces; and a controller for directing a Group IIIprecursor into the first reaction space at a first exposure and a GroupV precursor into the second reaction space at a second exposure.

In another aspect of the invention, Group III-V thin films are provided.In one embodiment, a Group III-V thin film is provided having a rootmean square of height differences of less than or equal to about 10nanometers (nm) when measured by atomic force microscopy (AFM). In someembodiments, the root mean square of height differences may be less thanor equal to about 5 nm, or less than or equal to about 2 nm. The GroupIII-V thin film may have a defect density of at most about 10¹⁰dislocations/cm². The Group III-V thin film may have a full-width athalf maximum of the omega scan of the (0002) or (10:12) x-rayreflections of less than or equal to about 600 arcseconds.

In embodiments, methods provided herein may be used to form Group III-Vthin films. In one embodiment, a light emitting diode (LED) having aGroup III-V thin film may be formed using methods provided herein. Inanother embodiment, a photovoltaic solar cell having a Group III-V thinfilm may be formed using methods provided herein. In another embodiment,a quantum well heterostructure device having a Group III-V thin film maybe formed using methods provided herein. In another embodiment, amultiple quantum well heterostructure having a Group III-V thin film maybe formed using methods provided herein.

INCORPORATION BY REFERENCE

All publications, patents, and patent applications mentioned in thisspecification are herein incorporated by reference to the same extent asif each individual publication, patent, or patent application wasspecifically and individually indicated to be incorporated by reference.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features of the invention are set forth with particularity inthe appended claims. A better understanding of the features andadvantages of the present invention will be obtained by reference to thefollowing detailed description that sets forth illustrative embodiments,in which the principles of the invention are utilized, and theaccompanying drawings of which:

FIG. 1 illustrates a method for forming a Group III-V thin film, inaccordance with an embodiment of the invention;

FIG. 2 schematically illustrates a cross-sectional top view of arotational system for the cyclic motion of one or more substratesthrough separated processing environments, in accordance with anembodiment of the invention. Processing environments A, B, C, and D maybe any of the environments described in the text, including a Group IIIenvironment, a Group V environment, a metrology environment, or ahydrogen-containing species (e.g., H₂, excited species of hydrogen)environment, in their various combinations. More than one location maybe of a given type of environment. In the illustrated embodiment of FIG.2, the environments are stationary and the substrates rotate through themultiple environments on a substrate carrier structure (or “susceptor”),which rotates about a central axis, in accordance with an embodiment ofthe invention;

FIGS. 3A-3E are schematic cross-sectional top views of thin filmdeposition systems having various configurations of a rotational systemfor the motion (e.g., cyclic motion) of one or more substrates throughseparated reaction spaces, in accordance with various embodiments of theinvention. FIG. 3A schematically illustrates a system including tworeaction spaces; FIG. 3B schematically illustrates a system includingthree reaction spaces; FIG. 3C schematically illustrates a systemincluding four reaction spaces, FIG. 3D schematically illustrates asystem including five reaction spaces; and FIG. 3E schematicallyillustrates a system including six reaction spaces, in accordance withan embodiment of the invention;

FIG. 4 is an optical emission spectrum of a radio-frequency inductivelycoupled plasma excitation of N₂ gas, where the strong majority ofoptical transitions are into the lowest energy band for excited N₂molecules (approximately 600 to 800 nm emission bands, referred to asthe 1^(st) positive series), in accordance with an embodiment of theinvention. The absence of strong emission in the approximate range 300to 400 nm, referred to as the 2^(nd) positive series, may be indicativeof a lack of higher energy excited N₂ molecules; and

FIG. 5 shows a structure having a Group III-V thin film formed over asubstrate, in accordance with an embodiment of the invention.

DETAILED DESCRIPTION OF THE INVENTION

While various embodiments of the invention have been shown and describedherein, it will be obvious to those skilled in the art that suchembodiments are provided by way of example only. Numerous variations,changes, and substitutions will now occur to those skilled in the artwithout departing from the invention. It should be understood thatvarious alternatives to the embodiments of the invention describedherein may be employed in practicing the invention.

Methods and systems provided herein enable formation of Group III-V thinfilms while reducing, if not eliminating, problems associated withcurrent systems and methods. In some embodiments, methods are providedfor forming Group III-V thin films while reducing, if not eliminating,contamination of Group III-V thin films. Thin films formed according tomethods and systems provided herein may be used in various applications,such as, for example, photovoltaic solar cell and light emitting diode(LED) devices and systems.

In embodiments, systems and methods are provided for forming Group III-Vthin films. In some embodiments, time and space co-divided systems andmethods are described in which a first precursor is brought in contactwith a substrate in a first reaction space and a second precursor isbrought in contact with the substrate in a second reaction space that isseparate from the first reaction space. In one embodiment, the firstprecursor is a Group III metal precursor, and exposure of the substrateto the Group III metal precursor forms a Group III metal thin film atsub-monolayer coverage. In another embodiment, the substrate is broughtin contact with one or more Group III metal precursors in the samereaction space or different reaction spaces, and exposure of thesubstrate to the one or more Group III metal precursors is separated byexposure of the substrate to a Group V precursor, a hydrogen-containingspecies, or other processing, such as, e.g., spectroscopies to determinethin film quality or composition.

The term “reaction space”, as used herein, may refer to any environmentsuitable for deposition of a material film or thin film on or over asubstrate, or the measurement of the physical characteristics of thematerial film or thin film. In one embodiment, a reaction space mayinclude a chamber. In another embodiment, a reaction space may include achamber in a system having a plurality chambers. In another embodiment,a reaction space may include a chamber in a system having a plurality offluidically separated chambers. In another embodiment, a system mayinclude multiple reactions spaces, wherein each reaction space isfluidically separated from another reaction space. In anotherembodiment, a reaction space may be suitable for conducting measurementson a substrate or a thin film formed on the substrate (or target).

The term “metal nitride”, as used herein, may refer to a materialcomprising one or more metals or one or more semiconductors, andnitrogen. In certain embodiments, a metal nitride (e.g., metal nitridethin film) may have the chemical formula M_(x)N_(y), wherein ‘M’designates a metal or a semiconductor, ‘N’ designates nitrogen, and ‘x’and ‘y’ are numbers greater than zero. In some embodiments, ‘M’ maycomprise one or more metals and/or semiconductors. In embodiments,M_(x)N_(y) may refer to a metal nitride, such as a Group III metalnitride (e.g., gallium nitride, indium nitride, aluminum galliumnitride, indium gallium aluminum nitride). In some embodiments, a metalnitride film or thin film may comprise other materials, such as, e.g.,chemical dopants. Chemical dopants may include p-type dopants (e.g.,magnesium, zinc) and n-type dopants (e.g., silicon, oxygen).

The terms “excited species” and “activated species”, as used herein, mayrefer to radicals, ions and other excited (or activated) speciesgenerated via application (or coupling) of energy to a reactant gas orvapor. In an embodiment, energy may be applied via a variety of methods,such as, e.g., ultraviolet radiation, microwave radiation, inductivecoupling and capacitive coupling, such as with the aid of a plasmagenerator. The plasma generator may be a direct plasma generator (i.e.,direct plasma generation) or a remote plasma generator (i.e., remoteplasma generation). In the absence of coupling energy, plasma generationis terminated. For remote plasma generation, plasma-excited species of aparticular vapor phase chemical (e.g., nitrogen-containing plasmaspecies) may be formed in a plasma generator in fluid communication with(or fluidically coupled to) a reaction space having a substrate to beprocessed. In another embodiment, energy may be applied by exposure of aspecies of gas to hot (or heated) surfaces or wires, where theinteraction of the gas with the heated surfaces or wires generatesexcited (or activated) species of the gas.

The term “nitrogen-containing species”, as used herein, may include,without limitation, nitrogen radicals, nitrogen ions, and excited (oractive) neutral species of nitrogen. In one embodiment, the gaseoussource of nitrogen-containing species may include, without limitation,N₂, NH₃, and/or hydrazine. In another embodiment, the gaseous source ofnitrogen-containing species may include mixtures of N₂ and H₂ gases. Inanother embodiment, excited nitrogen-containing species may be providedvia remote plasma generation or direct plasma generation. In anotherembodiment, excited nitrogen-containing species may be provided by thethermal disassociation of nitrogen-containing species by exposure to hotsurfaces or wires. Coupling energy to a mixture of N₂ and H₂ gases maygenerate excited molecular NH_(x), wherein ‘x’ is a number greater thanor equal to 1.

The term “hydrogen-containing species”, as used herein, may include,without limitation, hydrogen radicals, hydrogen ions, and excited (oractive) neutral species of hydrogen (H₂). In one embodiment,hydrogen-containing species includes H₂. In another embodiment, thegaseous source of hydrogen-containing species may include, withoutlimitation, H₂, NH₃, and/or hydrazine. In another embodiment, thegaseous source of hydrogen-containing species may include mixtures of H₂and N₂ gases. In another embodiment, excited hydrogen-containing speciesmay be provided via remote plasma generation or direct plasmageneration. In another embodiment, excited hydrogen-containing speciesmay be provided by the thermal disassociation of hydrogen-containingspecies by exposure to hot surfaces or wires. It will be appreciatedthat excited hydrogen-containing species may include neutralhydrogen-containing species, such as H₂.

The term “adsorption”, as used herein, may refer to chemical or physicalattachment of atoms or molecules on a surface, such as a substratesurface or a surface of a film or thin film on or over a substrate.

The term “substrate”, as used herein, may refer to any workpiece onwhich film or thin film formation is desired. Substrates may include,without limitation, silicon, silica, sapphire, zinc oxide, SiC, AlN,GaN, Spinel, coated silicon, silicon on oxide, silicon carbide on oxide,glass, gallium nitride, indium nitride and aluminum nitride, andcombinations (or alloys) thereof.

The term “surface”, as used herein, may refer to a boundary between thereaction space (or environment) and a feature of the substrate.

The term “monolayer”, as used herein, may refer to a single layer ofatoms or molecules. In one embodiment, a monolayer includes a monoatomicmonolayer (ML) having a thickness of one atomic layer. In anotherembodiment, a monolayer includes the maximum coverage of a particularspecies on a surface. In such a case, all individual members of thesurface adsorbed species may be in direct physical contact with thesurface of the underlying substrate, thin film or film. The term“sub-monolayer coverage”, as used herein, may refer to a layer of aparticular species at a coverage less than one monoatomic monolayer. Inone embodiment, a layer of a particular species at sub-monolayercoverage may permit additional adsorption of the species or anotherspecies. In another embodiment, sub-monolayer coverage may be referredto as “pre-wetting” coverage. For example, a layer of a Group III metal,such as gallium (Ga), indium (In) or aluminum (Al), may include Ga, Inor Al atoms collectively having a coverage of about 0.5 ML on a surface,which may be provided with respect to the maximum collective coverage ofGa, In or Al atoms on the surface. In one embodiment, the maximumcoverage of a species on a surface is determined by the attractive andrepulsive interaction between adsorbed species on the surface. Inanother embodiment, a layer of a species at a coverage of one monolayercannot permit additional adsorption of the species in the layer. Inanother embodiment, a layer of a particular species at a coverage of onemonolayer may permit the adsorption of another species in the layer.

The term “exposure”, as used herein, may refer to the product ofpressure (P) and time (t), i.e., P×t, wherein ‘P’ and ‘t’ are providedin units of ton and seconds, respectively. For example, a substrateexposed to a Group III metal precursor at a pressure of 1×10⁻⁶ ton for aperiod of 60 seconds is contacted with the Group III metal precursor atan exposure (or dosage) of 1×10⁻⁶ torr×60 seconds, or 60×10⁻⁶ torr*s, or60 Langmuir (L).

The term “precursor”, as used herein, may refer to a liquid or vaporphase chemical having a species of interest for deposition on asubstrate surface. A Group III metal precursor may include a chemicalcompound that includes one or more Group III metal atoms, such as one ormore of Ga, In and Al. A Group V precursor may include a chemical thatincludes one or more Group V atoms, such as one or more of nitrogen,arsenic and phosphorous. Upon interaction between a substrate surfaceand a Group III precursor or a Group V precursor, the Group IIIprecursor or the Group V precursor may dissociate to yield a Group IIIchemical (or adatoms of the Group III atom) or a Group V chemical (oradatoms of the Group V atom) on the substrate surface.

Methods for Forming Group III-V Thin Films

In one aspect of the invention, a method for forming a Group III-V thinfilm comprises providing a substrate in a first reaction space,contacting the substrate in the first reaction space with a Group IIImetal precursor (also “Group III precursor” herein) to form a Group IIImetal thin film, moving the substrate to a second reaction space, andcontacting the substrate in a second reaction space with a Group Vprecursor, thereby forming a Group III-V thin film. In one embodiment,contacting the substrate in the first reaction space with the Group IIIprecursor forms a Group III metal thin film at sub-monolayer coverage.

In some embodiments, prior to contacting the substrate with the Group Vprecursor, the substrate, including the Group III metal thin film on thesubstrate, is contacted with a hydrogen-contain species. In oneembodiment, the hydrogen-containing species includes H₂. In anotherembodiment, the hydrogen-containing species includes excited species ofhydrogen, including one or more of hydrogen cations, hydrogen anions andhydrogen radicals. In one embodiment, excited species of hydrogen may beprovided via remote plasma generation or direct plasma generation. Inanother embodiment, excited species of hydrogen may be provided by thethermal disassociation of molecular hydrogen by exposure of H₂ gas tohot surfaces or wires.

In one embodiment, the substrate may be contacted with ahydrogen-containing species in the first reaction space. In such a case,the first reaction space may be evacuated with the aid of purging and/orpumping prior to contacting the substrate with the hydrogen-containingspecies.

In one embodiment, prior to contacting the substrate in the secondreaction space with the Group V precursor, the substrate is moved to athird reaction space and contacted with a hydrogen-containing species inthe third reaction space. The third reaction space may be disposedin-between the first and second reaction spaces. In another embodiment,contacting a Group III metal thin film with excited species of hydrogenmay reduce multi-layer Group III islands to islands of monoatomic height(or thickness).

In embodiments, following the second reaction space, the substrate ismoved to the first reaction space. In other embodiments, following thesecond reaction space, the substrate is moved to a third reaction space.In one embodiment, in the third reaction space the substrate iscontacted with a Group III metal precursor. In another embodiment, inthe third reaction space the substrate is contacted with a Group IIImetal precursor that is different from the Group III metal precursorexposed to the substrate in the first reaction space. In anotherembodiment, following the third reaction space, the substrate is movedto one or more additional reaction spaces for separate exposure to aGroup III metal precursor and a Group V precursor. In anotherembodiment, in-between exposure to a Group III or Group V precursor, thesubstrate may be exposed to other species, such as hydrogen-containingspecies, which may aid in maintaining film stoichiometry and in reducingthin film contamination.

In some embodiments, after forming a Group III-V thin film on thesubstrate, the substrate, including the Group III-V thin film on thesubstrate, is contacted with a hydrogen-containing species. In anotherembodiment, the substrate is contacted with a hydrogen-containingspecies in the second reaction space. In such a case, the secondreaction space may be evacuated with the aid of purging and/or pumpingprior to contacting the substrate with a hydrogen-containing species. Inanother embodiment, the substrate is moved to a third reaction space andcontacted with a hydrogen-containing species in the third reactionspace. The third reaction space may be disposed in-between the first andsecond reaction spaces. In one embodiment, the third reaction space isdifference from the first and second reaction spaces.

Methods of embodiments of the invention may be used to form Group III-Vthin films, such as thin films including nitrogen and one or more ofaluminum (Al), gallium (Ga) and indium (In). In one embodiment, methodsare provided for forming GaN thin films. In another embodiment, methodsare provided for forming AlN thin films. In another embodiment, methodsare provided for forming InN thin films. In another embodiment, methodsare provided for forming AlGaN thin films. In another embodiment,methods are provided for forming AlInN thin films. In anotherembodiment, methods are provided for forming GaInN thin films. Inanother embodiment, methods are provided for forming InGaAlN thin films.

In one embodiment, in the first reaction space the substrate iscontacted with a single Group III metal precursor. In anotherembodiment, in the first reaction space the substrate is contacted withmultiple Group III metal precursors, such as one or more of Al, Ga andIn-containing precursors. In another embodiment, the substrate iscontacted with different Group III metal precursors in separate reactionspaces. In one embodiment, the substrate is contacted with a Group Vprecursor between exposures to Group III metal precursors.

In one embodiment, the first reaction space is different from the secondreaction space. In another embodiment, the first reaction space isfluidically separated from the second reaction space. In anotherembodiment, the first reaction space and the second reaction space areseparate pressure-regulated environments. In another embodiment, gasesfrom the first reaction space are prevented from entering the secondreaction space, and gases from the second reaction space are preventedfrom entering the first reaction space.

In one embodiment, a Group III-V thin film may have a thickness betweenabout 1 nanometer (“nm”) and 100 micrometers, or 1 nm and 10micrometers, or 10 nm and 1000 nm, or 20 nm and 500 nm. In anotherembodiment, a Group III-V thin film may have a thicknesses less thanabout 100 micrometers, or less than about 10 micrometers, or less thanabout 1000 nm, or less than about 500 nm, or less than about 100 nm. Inanother embodiment, Group III-V thin films may be formed at a growthrate of at least about 10 nm/hour, or at least about 100 nm/hour, or atleast about 1000 nm/hour, or at least about 5000 nm/hour. In anotherembodiment, Group III-V thin films may be formed at a growth rate ofless than about 5000 nm/hour, or less than about 1000 nm/hour, or lessthan about 500 nm/hour, or less than about 400 nm/hour, or less thanabout 300 nm/hour, or less than about 200 nm/hour, or less than about100 nm/hour.

With reference to FIG. 1, a method for forming a Group III-V thin filmis illustrated, in accordance with an embodiment of the invention. In afirst step 105, with the substrate disposed in a first reaction space,the substrate is contacted with a Group III metal precursor (e.g.,trimethyl gallium) to form a Group III metal thin film on the substrate.The substrate may be disposed in the first reaction space by moving thesubstrate (e.g., moving or rotating a susceptor having the substrate) tothe first reaction space or moving the first reaction space (e.g.,rotating the first reaction space) to the substrate. In one embodiment,the substrate is contacted for a time period no more than that requiredto form a Group III metal thin film at sub-monolayer coverage. Inanother embodiment, contacting the substrate in the first reaction spacewith the Group III metal precursor forms a layer of a Group III metalhaving a thickness less than about 1 monolayer (ML), or less than 0.95ML, or less than 0.9 ML, or less than 0.85 ML, or less than 0.8 ML, orless than 0.75 ML, or less than 0.7 ML, or less than 0.65 ML, or lessthan 0.6 ML, or less than 0.55 ML, or less than 0.5 ML, or less than0.45 ML, or less than 0.40 ML, or less than 0.35 ML, or less than 0.30ML, or less than 0.25 ML, or less than 0.20 ML, or less than 0.15 ML, orless than 0.10 ML, or less than 0.05 ML. In another embodiment,contacting the substrate in the first reaction space with the Group IIImetal precursor forms a layer of a Group III metal having a thickness upto about 0.05 ML, or 0.1 ML, or 0.15 ML, or 0.2 ML, or 0.25 ML, or 0.3ML, or 0.35 ML, or 0.4 ML, or 0.45 ML, or 0.5 ML, or 0.55 ML, or 0.6 ML,or 0.65 ML, or 0.7 ML, or 0.75 ML, or 0.8 ML, or 0.85 ML, or 0.9 ML, or0.95 ML, or 1 ML. In another embodiment, contacting the substrate in thefirst reaction space with the Group III metal precursor forms a layer ofa Group III metal at sub-monolayer coverage.

In one embodiment, an exposure of the Group III metal precursor may beselected to provide a Group III metal thin film at a predeterminedcoverage. Coverage may be assessed by a variety of spectroscopy tools(see below), such as x-ray photoelectron spectroscopy (XPS). Inachieving a predetermined coverage of a Group III metal thin film, itwill be understood that a trial-and-error approach may be used to findan exposure of the Group III metal precursor corresponding to thepredetermined coverage. For example, in one system it may be determinedthat achieving a Group III metal thin film coverage at 0.3 ML coveragerequires exposure of a substrate (also “target” herein) to a Group IIImetal precursor at about 1 L.

Next, in step 110, the substrate is disposed in a second reaction space.In some embodiments, the substrate may be moved to the second reactionspace. In other embodiments, the second reaction space may be moved(e.g., rotated) to the substrate. In one embodiment, movement of thesubstrate to the second reaction space comprises rotating a susceptorfrom the first reaction space to the second reaction space.

Next, in step 115, with the substrate in the second reaction space, thesubstrate, including the Group III metal thin film on the substrate, iscontacted with a Group V precursor to form a Group III-V-containing thinfilm. In one embodiment, the Group III-V-containing thin film includesGroup III-V species. In another embodiment, prior to contacting thesubstrate with the Group V precursor, the substrate may be contactedwith hydrogen-containing species (e.g., H₂, excited species ofhydrogen). The substrate may be contacted with hydrogen-containingspecies in the first reaction space, the second reaction space, or athird reaction space. In one embodiment, prior to contacting thesubstrate with hydrogen-containing species, a reaction space having thesubstrate may be evacuated with the aid of purging and/or pumping.

In one embodiment, the Group V precursor includes a nitrogen-containingspecies. In another embodiment, the Group V precursor includesplasma-excited species of nitrogen. In another embodiment, the Group Vprecursor includes active neutral species of nitrogen. In anotherembodiment, the Group V precursor includes active neutral species ofnitrogen comprises nitrogen species having the lowest excited state ofmolecular nitrogen (A³Σ_(u) ⁺). In one embodiment, the substrate iscontacted for a time period no more than that required to form a GroupIII-V thin film at sub-monolayer coverage. In another embodiment,contacting the substrate in the second reaction space with the Group Vprecursor forms a Group III-V thin film having a thickness less thanabout 1 ML, or less than 0.95 ML, or less than 0.9 ML, or less than 0.85ML, or less than 0.8 ML, or less than 0.75 ML, or less than 0.7 ML, orless than 0.65 ML, or less than 0.6 ML, or less than 0.55 ML, or lessthan 0.5 ML, or less than 0.45 ML, or less than 0.40 ML, or less than0.35 ML, or less than 0.30 ML, or less than 0.25 ML, or less than 0.20ML, or less than 0.15 ML, or less than 0.10 ML, or less than 0.05 ML. Inanother embodiment, contacting the substrate in the second reactionspace with the Group V precursor forms a Group III-V thin film having athickness up to about 0.05 ML, or 0.1 ML, or 0.15 ML, or 0.2 ML, or 0.25ML, or 0.3 ML, or 0.35 ML, or 0.4 ML, or 0.45 ML, or 0.5 ML, or 0.55 ML,or 0.6 ML, or 0.65 ML, or 0.7 ML, or 0.75 ML, or 0.8 ML, or 0.85 ML, or0.9 ML, or 0.95 ML, or 1 ML. In another embodiment, contacting thesubstrate in the second reaction space with the Group V precursor formsa Group III-V thin film at sub-monolayer coverage.

In some embodiments, plasma-excited species of nitrogen may include anitrogen and hydrogen-containing species formed by providing energy to amixture of N₂ and H₂ gases, NH₃, a mixture of N₂ and NH₃, hydrazine(N₂H₄), and/or a mixture of N₂ and N₂H₄. In one embodiment,plasma-excited species of nitrogen include NH_(x), wherein ‘x’ is anumber greater than or equal to 1. For example, plasma-excited speciesof nitrogen may include one or more of NH, NH₂ and NH₃, and ions andradicals of such species, such as, for example, NH⁺, NH₂ ⁺, NH₃ ⁺. Inanother embodiment, plasma-excited species of nitrogen are formed byinductively coupling energy to a mixture of N₂ and H₂ gases having aratio of N₂ and H₂ flow rates of about 0.5:1, or 1:1, or 2:1, or 3:1, or4:1, or 5:1. In another embodiment, plasma-excited species of nitrogenare formed by inductively coupling energy to a mixture of N₂ and H₂gases having an H₂ flow rate that is about ⅓ (or 0.333) of the total N₂and H₂ flow rate.

In embodiments, the substrate may be contacted with Group III and GroupV precursors until a Group III-V-containing thin film of predeterminedthickness is formed on the substrate.

With continued reference to FIG. 1, in step 120, the substrate is movedto the first reaction space or a third reaction space. In oneembodiment, the substrate is moved to the first reaction space andcontacted with a Group III metal precursor. In another embodiment, thesubstrate is moved to a third reaction space that is different from thefirst and second reaction spaces. In the third reaction space, thesubstrate may be contacted with a Group III metal precursor, a Group Vprecursor, or another species. For example, the substrate may becontacted with vapor phase chemical to aid in removing contaminants(e.g., carbon) from a Group III-V thin film formed on the substrate.

In one embodiment, the substrate is moved to successive reaction spaces(see below) until a thin film of predetermined thickness and compositionis formed.

In one embodiment, the substrate may be moved to the first reactionspace to repeat steps 105 to 120, as described above.

In one embodiment, after the second reaction space, the substrate may bemoved to one or more environments that include one or more thin filmdiagnostic tools, such as one or more thin film spectroscopy tools, toaid in assessing the physical characteristics (e.g., conductivity,thickness, long-range periodicity, composition) and/or quality of a thinfilm formed on the substrate. Spectroscopy tools may includereflection-absorption infrared spectroscopy (RAIRS), low-energy electrondiffraction (LEED) spectroscopy, x-ray photoelectron spectroscopy (XPS),Auger electron spectroscopy (AES), scanning probe microscopy (STM, AFM),near edge x-ray absorption fine structure (NEXAFS), spectral reflectanceand transmission, single wavelength reflectance and transmission,optical pyrometry (single wavelength, dual wavelength, or using spectralradiometry), emmisometry, ellipsometry, surface light scattering, andoptical polarimetry.

Systems for Forming Group III-V Thin Films

In another aspect of the invention, an apparatus for depositing a GroupIII-V thin film on a target is provided. The apparatus comprises a firstreaction space and a second reaction space, the first reaction spacefluidically separated from the second reaction space. The apparatusfurther includes a susceptor or substrate holder for bringing a target(or substrate) in contact with each of the first and second reactionspaces. In one embodiment, the apparatus includes a controller (see,e.g., FIG. 2) for directing a Group III precursor into the firstreaction space at a first exposure and a Group V precursor into thesecond reaction space at a second exposure. In another embodiment, thefirst exposure is for providing a layer of a Group III metal atsub-monolayer (or pre-wetting) coverage.

In embodiments, a number of the practical problems with the state of theart for the deposition of binary semiconducting thin films may bemitigated by separating the environment (or reaction space) in which theGroup III metal atoms are deposited onto a substrate from theenvironment in which these adsorbed metal atoms are exposed to a GroupV-containing precursor gas to form the Group III-V thin film orcompound. In one embodiment, the substrate is moved between depositionreaction spaces (or environments) cyclically to deposit a film of apredetermined thickness. FIG. 2 is an example of a system of linkedsequential processing environments, which may be constructed for thispurpose.

In one embodiment, this technique may mitigate the gas phase reactionbetween Group III and Group V-containing precursor gases, because theGroup III and Group V precursor gases will not be present in significantamounts in the same reaction volume due to flow and pressure control ofeach individual reaction space. Maintaining separate environmentsfurther allows for optimization of the environment for the delivery ofGroup III adatoms to the surface, and a separate environment (orreaction space) where the delivery of the Group V precursor is optimizedfor surface reaction to form the desired III-V compound. In the case ofInGaAlN thin films, the Group III metal delivery may be optimized foruse of metal organic precursors such as (here described for the case ofgallium; similarly for other Group III metals) trimethylgallium,triethylgallium, diethylgallium chloride, and coordinated galliumhydride compounds, e.g., dimethylgallium hydride, etc.; thermalevaporation of the Group III material; or gaseous Group III chlorides orGroup III halides, among other methods. In one embodiment, in the caseof InGaAlN thin films, the nitridation environment may be optimized forvarious methods to deliver active nitrogen to the wafer surface,including plasma excitation or thermal disassociation ofnitrogen-containing species.

The separate deposition environments for Group III and Group V elementsmay enable incompatible processes in each of the independentenvironments. For example, different gas flows and pumping speeds may beused in the Group III and Group V environments. Additionally, mechanismsuseful for the creation of reactive Group V species but detrimental tothe delivery of Group III precursors, for example ionization anddisassociation via plasma excitation, may be used without constraintsdue to the absence of Group III precursors in the Group V reactionenvironment.

The various molecular excitation states of N₂ gas may be characterizedby the use of optical emission spectroscopy. See, for example, Theidentification of molecular spectra, R. W. B. Pearse and A. G. Gaydon,Chapman and Hall, 1976, which is entirely incorporated herein byreference. Optical emissions are the result of transitions from a higherenergy excited state to a lower energy state. For the N₂ molecule, thegroup of transitions in the region of approximately 600 nanometer (nm)to 800 nm (which may be referred to as the ‘1^(st) positive series’ ofN₂ emission lines) result from transitions which terminate in a band ofstates with a minimum excitation energy of approximately 6 electronvolts (eV). This is the lowest internal energy of the excited states ofthe neutral N₂ molecule. An optical emission spectrum from aninductively-coupled plasma excitation of N₂ gas is shown in FIG. 4.These emission characteristics indicate that a strong majority of theexcited N₂ molecules in this population has approximately 6 eV ofinternal energy. In one embodiment, this excitation of N₂ gas may beused for InGaAlN thin film deposition.

Because of the separate Group III and Group V deposition environments,the Group III metal adatoms are not instantaneously reacted with Group Vatoms. The technique results in an increase in the surface mobility ofadsorbed metal atoms, which promotes improved crystalline quality byallowing additions to the growing surface to be made at highlycoordinated, low energy sites. The technique in general promotestwo-dimensional growth where growth takes place at atomic step edges.See, for example, “2.6 μm/hr High-Speed Growth of GaN by RF-MolecularBeam Epitaxy and Improvement of Crystal Quality by Migration EnhancedEpitaxy,” D. Sugihara et al., Phys. Stat. Sol. (a) 176, 323 (1999),which is entirely incorporated herein by reference. In one embodiment,this technique may promote the growth of two-dimensional islands (i.e.,islands having a thickness of one atomic layer). In another embodiment,this technique may promote the growth of three-dimensional islands(i.e., islands having a thickness of a plurality of atomic layers).

Methods of embodiments of the invention may enable the use of lowersubstrate temperatures than is typical in the state of the art MOCVD dueto the improved crystalline quality resulting from the increased surfacemigration of metal adatoms. For example, Sugihara et al. report 750° C.for their GaN growths, compared to approximately 1050° C. for typicalMOCVD. Reduced processing temperatures relative to the state of the artenable the use of less costly substrates and a simplified reactordesign.

Separation of the Group III and Group V deposition environmentsnecessarily creates a situation where the surface of the substrate willhave an excess of Group III atoms for a portion of the deposition cycle.Group III metals, in particular Ga and In, may form droplets on thesubstrate surface when the Group III element is in excess of thestoichiometric amount of the Group V element needed to form the desiredIII-V compound. For example see D. Sugihara et al., and “EpitaxialGrowth of GaN on Sapphire (0001) Substrates by Electron CyclotronResonance Molecular Beam Epitaxy,” S. H. Cho et al., Jpn. J. Appl. Phys.34, L236 (1995), which is entirely incorporated herein by reference.Group III metal droplets which do not dissolve during processing andremain in the film may damage the optoelectronic material properties andmay be incompatible with device manufacture.

Methods of embodiments of the invention may enable Group III metaldroplet formation to be mitigated, if not eliminated, by depositing asub-monolayer coverage of the Group III metal during each cycle. At thiscoverage, the Group III metal thickness may be less than the wettinglayer thickness, and metal droplet formation may be suppressed.Additionally, sub-monolayer coverage of metal adatoms reduces the numberof interactions between the adatoms, reducing their self-scattering andincreasing the adatom surface mobility.

In embodiments, hydrogen-containing species may be used during theformation of the Group III-V thin film on a substrate. Thehydrogen-containing species may be maintained in a separate environmentfrom the Group III and Group V reaction environments, and may beemployed after Group III environment, after Group V environment, orboth. In one embodiment, hydrogen-containing species may be brought incontact with a substrate, a Group III metal film, or a Group III-V filmon the substrate in a reaction space that is separate from a reactionspace having a Group III or Group V precursor. In an embodiment, anenvironment comprising hydrogen-containing species may be employedsequentially after a Group V reaction space, where excess Group IIIatoms or droplets will be converted to Group III halides, e.g., GaH₃.Group III halides may be volatile, and droplets will be removed from thesurface each cycle. This allows the growth surface to be stoichiometricat the beginning of each deposition cycle. In another embodiment, anenvironment comprising hydrogen-containing species may be employedsequentially after a Group III reaction space, where the excited speciesof hydrogen may reduce multi-layer Group III islands to islands ofmonoatomic height (or thickness).

In one embodiment, an additional benefit of exposing the film tohydrogen-containing species is that activated species of hydrogen mayscavenge (or getter) carbon atoms and/or hydrocarbon groups, which aredue to residual contamination from the alkyl groups present in metalorganic precursors. See, for example, Bornscheuer et al., “Production ofAtomic Hydrogen and its Use for the Growth of GaN with Low CarbonLevel,” Phys. Stat. Sol. (a) 159, 133 (1997), and Kim et al., “Effect ofHydrogen on GaN Growth by Remote Plasma-Enhanced Metal-Organic ChemicalVapor Deposition,” Phys. Stat. Sol. (a) 176, 337 (1999), which areentirely incorporated herein by reference. In another embodiment,plasma-excited hydrogen-containing species may be used to scavenge andremove one or more impurity species selected from carbon, sulfur andoxygen. This may advantageously minimize, if not eliminate, furthercontamination of the substrate or thin film over the substrate.

In embodiments, an additional environment may be maintained where thinfilm properties may be measured in-situ. In this environment nodeposition occurs and the optical viewports, lens systems,spectroscopies, and other ports needed to make stable and accuratemeasurements may be maintained. Measurements which could be performed inthis environment include, but are not limited to, reflection-absorptioninfrared spectroscopy (RAIRS), low-energy electron diffraction (LEED)spectroscopy, x-ray photoelectron spectroscopy (XPS), Auger electronspectroscopy (AES), scanning probe microscopy (STM, AFM), near edgex-ray absorption fine structure (NEXAFS), spectral reflectance andtransmission, single wavelength reflectance and transmission, opticalpyrometry (single wavelength, dual wavelength, or using spectralradiometry), emmisometry, ellipsometry, surface light scattering, andoptical polarimetry. Thin film data gathered from measurements, such asthose made with the aid of tools (e.g., spectrometers) provided herein,may include thickness, dielectric constant, conductivity (orresistivity), optical attenuation constant, temperature, and emissivity.Such data may be used in a real-time closed loop control system, whereaspects of the deposition environments may be actuated to maintain themeasured parameters within a specified tolerance. This arrangement mayprovide for thin film property optimization, device performanceoptimization, thin film deposition parameter optimization (e.g.,optimization of reaction space pressures, deposition temperatures, flowrates), run-to-run repeatability, system-to-system repeatability andmatching, and improved yield of manufactured goods.

FIG. 3 depicts several examples of simplified representations of variousconfigurations possible of a rotational system for the cyclic motion ofone or more substrates through separated processing environments, wherethe environments are any of those described.

To summarize, the separation of the Group III and Group V depositionenvironments to form a III-V compound, and the cyclic motion of asubstrate through these separated environments, where the formation ofmetal droplets is suppressed by using sub-monolayer coverages of metaladatoms per cycle, may result in a high quality crystalline Group III-Vcompound formed via a relatively low temperature process withoutdetrimental gas phase reactions between the Group III and Group Vprecursors. Optionally, an exposure to excited hydrogen-containingspecies may be done in a separate environment to assist in managingmetal droplet formation and/or reduce carbon contamination. Optionally,in-situ thin film measurements may be done in a separate environmentwhich is maintained for optimal stability and repeatability of themeasurements, and the data from these measurements may be used forreal-time closed loop control of the deposition and hydrogenenvironments.

In embodiments of the invention, controllers and systems are providedfor controlling and regulating Group III-V thin film formation. In oneembodiment, a control system is provided to control various processparameters, such as, for example, substrate and/or substrate holder (orsusceptor) temperature, reactor pressure, reaction space pressure,reaction chamber pressure, plasma generator pressure, the flow rate ofgas (e.g., N₂) into a plasma generator, the flow rate of gas (e.g.,metalorganic species) into a reaction space, the rate at which thesubstrate is moved from one reaction space to another, the rate at whichthe substrate rotates during thin film formation, power to a plasmagenerator (e.g., direct current or radio frequency power), and a vacuumsystem in fluid communication with the reaction chamber. The vacuumsystem may comprise various pumps configured to provide vacuum to thereaction chamber, such as, e.g., one or more of a turbomolecular(“turbo”) pump, a cryopump, an ion pump and a diffusion pump, inaddition to a backing pump, such as a mechanical pump.

Group III-V Thin Films

In another aspect of the invention, Group III-V thin films are provided.Group III-V thin films may be formed according to methods providedherein. The Group III-V thin film may include one or more materialsselected from gallium nitride, indium gallium nitride, aluminum nitride,indium nitride, aluminum gallium nitride, indium gallium aluminumnitride, or combinations thereof.

With reference to FIG. 5, a structure (or device) is shown having aGroup III-V thin film 505 formed on a substrate 510, in accordance withan embodiment of the invention. The thin film 505 may be formedaccording to any method provided herein, such as the methods discussedin the context of FIG. 1. In addition, the thin film 505 may be formedusing any device, apparatus or system provided herein, such as theapparatus of FIG. 2 or any of the systems of FIG. 3. The substrate 510may be selected from silicon, silica, sapphire, zinc oxide, SiC, AlN,GaN, Spinel, coated silicon, silicon on oxide, silicon carbide on oxide,glass, gallium nitride, indium nitride and aluminum nitride, andcombinations (or alloys) thereof. The substrate 510 may be a chemicallydoped substrate (e.g., doped n-type or p-type), or intrinsic.

The device of FIG. 5 may be suitable for various applications. Forexample, the thin film 505 of FIG. 5 may be employed in electronicsdevices, such as photovoltaic solar cells. The Group III-V thin film 505may be used in various semiconductor applications or devices, such asoptoelectronic applications, including light emitting diodes (LED)(e.g., GaN based violet laser diodes); field effect transistors (FET),including metal-oxide semiconductor FET (MOSFET) and metal semiconductorFET (MESFET) devices; and transistors, including high electron mobilitytransistors (HEMT). The compositions and thicknesses of the Group III-Vthin film 505 and substrate 510 may be selected in accordance withdevice applications.

In some embodiments, Group III-V thin films formed according to methodsprovided herein may have defect (e.g., misfit dislocations, such asthreading and/or edge dislocation) densities of at most about 10⁶dislocations/cm², or at most about 10⁷ dislocations/cm², or at mostabout 10⁸ dislocations/cm², or at most about 10⁹ dislocations/cm², or atmost about 10¹⁰ dislocations/cm². In some embodiments, defect densitiesof Group III-V thin films may be between about 10⁶ dislocations/cm² and10¹⁰ dislocations/cm².

In some embodiments, Group III-V thin films (e.g., GaN thin films)formed according to methods provided herein may have a root mean squareof the height differences measured by atomic force microscopy (AFM), ofless than or equal to about 0.5 nanometers (“nm”), or less than or equalto about 1 nm, or less than or equal to about 1.5 nm, or less than orequal to about 2 nm, or less than or equal to about 2.5 nm, or less thanor equal to about 3 nm, or less than or equal to about 3.5 nm, or lessthan or equal to about 4 nm, or less than or equal to about 4.5 nm, orless than or equal to about 5 nm, or less than or equal to about 6 nm,or less than or equal to about 7 nm, or less than or equal to about 8nm, or less than or equal to about 9 nm, or less than or equal to about10 nm.

The crystalline quality of Group III-V thin films formed according tomethods provided herein may be probed by an x-ray diffractionmeasurement, such as the full-width at half maximum of the omega scan ofthe (0002) or (10 12) x-ray reflections. In some embodiments, thefull-width at half maximum of the (0002) or (10 12) crystallographicreflections of Group III-V thin films formed according to methodsprovided herein may be less than or equal to about 100 arcseconds, orless than or equal to about 200 arcseconds, or less than or equal toabout 300 arcseconds, or less than or equal to about 400 arcseconds, orless than or equal to about 500 arcseconds, or less than or equal toabout 600 arcseconds.

In some embodiments, an indium-containing Group III-V thin film may havea fractional indium concentration, In_(x)Z_((1-x))N (“InZN”), wherein‘x’ is a number greater than zero and less than one, ‘N’ is nitrogen,and ‘Z’ is a Group III species. In some embodiments, “x’ may be at mostabout 0.99, or at most about 0.9, or at most about 0.8, or at most about0.7, or at most about 0.6, or at most about 0.5, or at most about 0.4,or at most about 0.3, or at most about 0.2, or at most about 0.1. Insome embodiments, InZN thin films may comprise one or more layers of alight emitting diode (LED) heterostructure device. In some embodiments,InZN thin films may comprise one or more layers of a quantum wellheterostructure device. In some embodiments, InZN thin films maycomprise one or more layers of a multiple quantum well heterostructuredevice.

In some embodiments, InGaN thin films formed according to methodsprovided herein may have a fractional indium concentration,In_(x)Ga_((1-x))N, wherein ‘x’ is a number greater than zero and lessthan one. In some embodiments, “x’ may be at most about 0.99, or at mostabout 0.9, or at most about 0.8, or at most about 0.7, or at most about0.6, or at most about 0.5, or at most about 0.4, or at most about 0.3,or at most about 0.2, or at most about 0.1. In some embodiments, InGaNthin films may comprise one or more layers of a light emitting diode(LED) heterostructure device. In some embodiments, InGaN thin films maycomprise one or more layers of a quantum well heterostructure device. Insome embodiments, InGaN thin films may comprise one or more layers of amultiple quantum well heterostructure device.

Example

A system, such as the system of FIG. 2, includes four reaction spacesdisposed in relation to one another adjacently along a circumference. Asubstrate, heated to a temperature of about 700° C., is provided in afirst reaction space and contacted with trimethylgallium at a pressureof about 0.5 Torr. The first exposure of trimethylgallium is sufficientto form a gallium thin film at a coverage of about 0.5 ML. Next, thesubstrate, heated to a temperature of about 700° C., is rotated to asecond reaction space and contacted with excited hydrogen-containingspecies, including hydrogen radicals and ions, at a pressure of about0.5 Torr. Excited hydrogen-containing species are formed by providingplasma power of about 500 Watts to H₂. Next, the substrate, heated to atemperature of about 700° C., is rotated to a third reaction space andcontacted with a mixture of N₂ and H₂, at a pressure of about 0.5 Torr.Plasma power of about 500 Watts is provided to the mixture to generateexcited species of N₂ and H₂. Plasma power is sufficient to generateactive neutral species of nitrogen having the lowest excited state ofmolecular nitrogen (A³Σ_(u) ⁺). Next, the substrate, heated to atemperature of about 700° C., is rotated to a fourth reaction space andcontacted with excited hydrogen-containing species, including hydrogenradicals and ions, at a pressure of about 0.5 Torr. Next, the substrateis rotated to the first reaction space, and the steps above are repeatedto provide a Group III-V thin film having, in total, a thickness ofabout 4000 nanometers (“nm”).

Method and systems of embodiments of the invention may be combined with,or modified by, other systems and methods. For example, methods andsystems of embodiments of the invention may be combined with, ormodified by, methods and systems described in U.S. Pat. No. 6,305,314,U.S. Pat. No. 6,451,695, U.S. Pat. No. 6,015,590, U.S. Pat. No.5,366,555, U.S. Pat. No. 5,916,365, U.S. Pat. No. 6,342,277, U.S. Pat.No. 6,197,683, U.S. Pat. No. 7,192,849, U.S. Pat. No. 7,537,950, U.S.Pat. No. 7,326,963, U.S. Pat. No. 7,491,626, U.S. Pat. No. 6,756,318,U.S. Pat. No. 6,001,173, U.S. Pat. No. 6,856,005, U.S. Pat. No.6,869,641, U.S. Pat. No. 7,348,606, U.S. Pat. No. 6,878,593, U.S. Pat.No. 6,764,888, U.S. Pat. No. 6,690,042, U.S. Pat. No. 4,616,248, U.S.Pat. No. 4,614,961, U.S. Patent Publication No. 2006/0021574, U.S.Patent Publication No. 2007/0141258, U.S. Patent Publication No.2007/0186853, U.S. Patent Publication No. 2007/0215036, U.S. PatentPublication No. 2007/0218701, U.S. Patent Publication No. 2008/0173735,U.S. Patent Publication No. 2009/0090984, U.S. Patent Publication No.2010/0210067, Patent Cooperation Treaty (“PCT”) Publication No.WO/2003/041141, PCT Publication No. WO/2006/034540 and PCT PublicationNo. WO/2010/091470, and PCT Publication No. WO/2010/092482, which areentirely incorporated herein by reference.

It should be understood from the foregoing that, while particularimplementations have been illustrated and described, variousmodifications can be made thereto and are contemplated herein. It isalso not intended that the invention be limited by the specific examplesprovided within the specification. While the invention has beendescribed with reference to the aforementioned specification, thedescriptions and illustrations of embodiments of the invention hereinare not meant to be construed in a limiting sense. Furthermore, it shallbe understood that all aspects of the invention are not limited to thespecific depictions, configurations or relative proportions set forthherein which depend upon a variety of conditions and variables. Variousmodifications in form and detail of the embodiments of the inventionwill be apparent to a person skilled in the art. It is thereforecontemplated that the invention shall also cover any such modifications,variations and equivalents.

1. A method for forming a thin film, comprising: contacting a substratein a first reaction space with a first precursor to form a first metallayer at sub-monolayer coverage; and contacting the substrate in asecond reaction space with a Group V precursor, wherein the Group Vprecursor comprises a nitrogen containing species and wherein thenitrogen-containing species comprises active neutral species ofnitrogen; wherein the first precursor comprises at least one of a GroupIII element.
 2. The method of claim 1, wherein the first reaction spaceis fluidically separated from the second reaction space.
 3. The methodof claim 1, wherein contacting the substrate with the first precursorforms a non-self limiting layer of the first metal layer over thesubstrate.
 4. The method of claim 1, wherein the active neutral speciesof nitrogen comprises nitrogen species having the lowest excited stateof molecular nitrogen (A³:Σ_(u) ⁺).
 5. The method of claim 4, whereinthe nitrogen-containing species comprises one of N₂, NH₃, N₂H₂, or amixture of N₂ and H₂.
 6. The method of claim 1, wherein the secondprecursor comprises plasma activated species of a Group V containingmolecule.
 7. The method of claim 1, wherein the Group V precursorcomprises plasma activated nitrogen-containing species.
 8. The method ofclaim 1, wherein contacting the substrate in the second reaction spacewith the Group V precursor comprises providing a Group V precursor and ahydrogen containing species.
 9. The method of claim 1, wherein the firstprecursor comprises a gallium containing species.
 10. The method ofclaim 1, wherein the first precursor comprises one or more speciesselected from boron (B), aluminum (AI), gallium (Ga) and indium (In).11. The method of claim 1, wherein the first precursor comprises ametalorganic species.
 12. The method of claim 1, wherein contacting thesubstrate in the first reaction space with the first precursor forms alayer of a first metal layer having a thickness up to about 1 monolayer(ML).
 13. The method of claim 16, wherein contacting the substrate inthe second reaction space with the Group V precursor forms a Group III-Vthin film having a thickness less than 1 ML.
 14. The method of claim 1,wherein the thin film is a Group III metal nitride thin film.
 15. Themethod of claim 1, further comprising heating the substrate whileforming the thin film.
 16. The method of claim 1, further comprisingcontacting the first metal layer with hydrogen-containing species in athird reaction space prior to contacting the substrate in the secondreaction space with the Group V precursor.
 17. The method of claim 16,wherein the hydrogen-containing species are selected from hydrogen (H₂)and excited species of hydrogen.
 18. The method of claim 1, furthercomprising contacting the thin film with hydrogen-containing species ina third reaction space.
 19. The method of claim 18, wherein thehydrogen-containing species are selected from hydrogen (H₂) and excitedspecies of hydrogen.
 20. The method of claim 1, wherein the Group III-Vthin film comprises In_(x)Ga_((1-x))N, wherein ‘x’ is a number greaterthan 0 and less than 1.